sql - 如何在组中查找重复项 - SQL 2008

Question

我有一个包含以下数据的表 (MyTable)。 (按Order_No,Category,Type排序)

Order _No   Category    Type    
Ord1    A   Main Unit   
Ord1    A   Other   
Ord1    A   Other   
Ord2    B   Main Unit   
Ord2    B   Main Unit   
Ord2    B   Other   

我需要做的是，扫描表格，看看是否有任何“类别”有多个“主要单位”。 如果是这样，请对整个类别发出警告。预期结果应如下所示。

Order _No   Category    Type      Warning
Ord1    A   Main Unit   
Ord1    A   Other   
Ord1    A   Other   
Ord2    B   Main Unit     More than one Main Units
Ord2    B   Main Unit     More than one Main Units
Ord2    B   Other     More than one Main Units

我尝试了几种方法(使用子查询)来获得结果，但没有成功。请帮忙!!

(Case
 When (Select t1.Category
             From MyTable as t1 
    Where  MyTable.Order_No = t1.Order_No
                    AND MyTable.Category = t1. Category
        AND  MyTable.Type = t1.Type
               AND  MyTable.Type = ‘Main Unit’
    Group by t1. t1.Order_No, t1. Category, t1.Type
Having  Count(*) >1) = 1
Then ‘More than one Main Units’
Else ‘’ End ) as Warning

Answer 1

一个选项是使用 COUNT() OVER() 来计算主要单位，按类别划分；

SELECT Order_No, Category, Type, 
  CASE WHEN COUNT(CASE WHEN Type='Main Unit' THEN 1 ELSE NULL END) 
            OVER (PARTITION BY Category) > 1 
       THEN 'More than one Main Units' ELSE '' END Warning
FROM MyTable

An SQLfiddle to test with .